1. Field of the Invention
The present invention relates generally to medical devices and more particularly to an improved catheter system having a work element coupled to a drive cable disposed within a lumen of a flexible tubular catheter body.
2. Description of the Background Art
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheromas or plaque, on the walls of blood vessels. Such deposits occur in both the peripheral blood vessels, which feed the limbs of the body, and the coronary vessels, which feed the heart. When deposits accumulate in localized regions of a blood vessel, stenosis, or narrowing of the vascular channel, occurs. Blood flow is restricted and the person""s health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits are known, including balloon angioplasty, in which a balloon-tipped catheter is used to dilate a region of atheroma; atherectomy, in which a blade or cutting bit is used to sever and remove the atheroma; spark gap reduction, in which an electrical spark burns through the plaque; and laser angioplasty, in which laser energy is used to ablate at least a portion of the atheroma. In order to facilitate treatment of the stenosis, it is often desirable to obtain a visual image of the interior of the blood vessel within the region of interest. Catheters having imaging elements such as ultrasonic transducers are often used to obtain these images.
In many cases, catheter systems having imaging or interventional devices will include a rotatable drive cable disposed within the flexible catheter body. Catheters of this type will have some type of work element fixed to the distal end of the drive cable. In imaging systems, the work element is typically an ultrasonic transducer or a movable mirror associated with an ultrasonic transducer.
An exemplary catheter system having a rotating ultrasonic transducer coupled to a drive cable is disclosed in U.S. Pat. No. 4,794,931, the disclosure of which is incorporated herein by reference. In this system, a drive cable disposed within a flexible tubular catheter body is used to rotate an ultrasonic transducer about an axis parallel to the catheter body. The ultrasonic transducer is thereby caused to scan a region of the blood vessel in a plane normal to the catheter body.
In yet another exemplary catheter system of particular importance to the present invention, a catheter body is provided with a guidewire engagement sheath design, where the catheter is introduced over a separate (moveable) guidewire. A catheter system of this type is disclosed in U.S. Pat. No. 5,203,338, which is fully incorporated herein by reference. In this particular catheter system, the catheter body has a guidewire lumen attached at the distal end of the catheter body. The guidewire lumen and the primary lumen are separated by a wedge, which ensures that the drive cable does not proceed beyond the primary lumen and into the guidewire lumen.
A catheter of the type having a guidewire engagement is used as follows. A guidewire is advanced into the patient until it lies within a region of interest, typically a region of stenosis within the blood vessel. After the guidewire is positioned, the proximal end of the guidewire is fed into the guidewire lumen of the catheter. The catheter is then advanced into the patient over the guidewire. Advancement of the catheter into the patient continues until the primary lumen distal region lies within the blood vessel in the region of interest. A suitable work element, such as a rotatable imaging core, may be delivered while positioned in the primary lumen.
A general concern in the development of each type of catheter system described above, and in catheter system development in general, is the ability to achieve consistency in reliability and performance among catheters employing a particular system. In response to this concern, approaches have been identified which may provide techniques for improving common components of these catheter systems to provide consistent reliability and performance.
One such approach of particular interest to the present invention, includes improvement of the hub assembly. The hub assembly provides, among other things, electrical coupling to the rotating transducer or other work element. Rotation of the transducer element makes it necessary to transmit an electrical signal through a fixed ferrite wire to a transducer lead wire disposed within the rotating drive cable. The signal is transmitted between the fixed and rotating wires through the well-known electrical process of induction. Generally, this process includes using two ferrites separated by a small air gap, where the first ferrite rotates relative to a second fixed ferrite. The first ferrite, when charged, produces an electromagnetic field. The second ferrite, in close proximity to the first ferrite and its electromagnetic field, causes the introduction of inductance into the circuit. The gap is generally necessary to remove the negative effects of friction which occur whenever a rotating body contacts a fixed body. However, as in most rotary transformers, there are losses of power and other inefficiencies inherent in this transmission. For example, it is generally difficult without labor intensive and expensive manufacturing processes, to provide a consistent gap size. Without a consistent gap, the output performance of the transformer can vary between hub assemblies. Moreover, it can be difficult to ensure that the rotating ferrite rotates with enough precision to avoid inadvertently contacting the fixed ferrite.
A number of other approaches for improving catheter systems are directed at the drive cable. The drive cable is coupled via a drive shaft to a drive motor. The drive cable runs substantially the length of the catheter body, and serves as a flexible, torque-transmitting element to rotate the electrical transducer. The drive cable is constructed with coils in order to provide torsional stiffness and flexibility. This enables the drive cable to traverse the tortuous lumen of the human vascular system. A drive cable, which may include transducer lead wires surrounded in a coaxial fashion by a coiled cable body, is disclosed in U.S. Pat. No. 5,503,155, the disclosure of which is incorporated herein by reference.
One potential drawback to the drive cable described above is its susceptibility to stretching. Stretching of the drive cable is typically encountered during removal procedures, during pullback sequences, where the imaging core is retracted within the flexible catheter body to obtain longitudinal imaging sequences, or else during flushing operations. Upon removing the catheter from the intravascular lumen, the user must xe2x80x9cpull backxe2x80x9d on the proximal end of the catheter body. Generally, movement of the catheter can be restricted when the catheter body encounters friction between the catheter body and the walls of the intravascular lumen. When movement of the catheter body is restricted in this manner, the coils of the drive cable can stretch in a manner similar to coils of a spring. The coils can also be stretched apart when the catheter body is being flushed-out with a flushing fluid. In this case, the flushing fluid creates a piston effect on the coils and work element, thus spreading the coils apart.
While a stretchable drive cable may be advantageous for some purposes, it can also be problematic. Transducer lead wires, disposed and anchored within the drive cable lumen, do not have the ability to stretch and when subjected to tensile forces, the transducer lead wires tend to break which creates a break in the electrical continuity of the system.
Other improvements to catheter systems may include re-directing flushing fluids from exiting through a side port positioned at the distal end of the primary lumen. Generally, the side exit port works well, however, the side exit port can be a nuisance in a clinical setting since it is difficult to know which way the side exit port is pointing during flushing procedures.
For these reasons, it would be desirable to provide an improved catheter system for use with internal work elements, such as ultrasonic imaging transducers. It would be particularly desirable to provide a catheter system that has an improved hub assembly that permits efficient electrical induction to provide a more consistent and reliable signal to the transducer element. It would be further desirable if the drive cable of the catheter were configured to prevent the internal electrical transmission line from breaking should the drive capable be forced to stretch, such as when the user is pulling back or flushing the catheter body. It would be still further desirable if the catheter body were formed with a primary lumen and a guidewire lumen that would provide a distal exit port for the egress of flushing fluids parallel to the direction of blood flow. At least some of these objectives and more are met by the invention described hereinafter.
The present invention is directed to an improved catheter system having a work element coupled to a drive cable disposed within a lumen of a flexible tubular catheter body. The work element generally includes an ultrasonic imaging transducer. One advantageous improvement described in more detail below, includes a reconfiguration of ferrites in the hub assembly, such that a gap, typical between the ferrites, is reduced or eliminated. In reducing or eliminating the gap it is meant that the average clearance between two facing surfaces of the ferrites will be less than 0.0005 in., preferably less than 0.0002 in., and most preferably less than 0.0001 in. In reducing or eliminating the gap clearance in this manner, manufacture of the hub assembly can be done with less precision, which makes the overall fabrication process simpler and less expensive. Moreover, by reducing or eliminating the gap clearance, the inductive transmission of the electrical signal can be accomplished with more efficiency and with reduced transmission losses.
Another improvement lessens the potential for tensile failure of the electrical transmission lines when subjected to stretching. In one embodiment, a strain relief member is provided proximate and parallel to the transmission lines. The transmission lines are arranged slacked relative to the strain relief member. Thus, when the transmission lines and strain relief member are subjected to stretching forces, usually caused by either flushing and/or pull-back operations, the strain relief member and not the transmission lines is subjected to the forces. Accordingly, the transmission lines are protected. In an alternative embodiment, a portion of the transmission lines is looped in a manner similar to the coils of a spring. In this configuration, the lines can extend when subjected to a pulling force and retract when the force is removed.
Another improvement to the catheter system includes a drive cable fabricated as a multi-layered structure where each layer includes a counter-wound coil. The coils may either expand or contract as the drive cable rotates which increases the interference between the multiple layers and thus increases the torque transmission capability of the drive cable. At the same time, the multi-layered coil structure allows the drive cable to maintain the requisite flexibility.
In yet another improvement, the distal tip of the catheter body has a lumen positioned between the catheter lumen and the guidewire lumen to allow flushing fluid or other fluids to be released through a distal port of the guidewire lumen.
Another improvement to the catheter system may include catheter tubing having multiple tubing portions of varying material strengths, stiffnesses, and/or wall thicknesses. For example, a tubing portion may be provided having an intermediate tubing stiffness relative to a stiff proximal portion of the catheter body and a highly flexible distal portion. The intermediate portion may be placed between the proximal and distal portions to provide a transitional area. The transitional area increases the practitioner""s ability to advance the catheter into a body lumen without kinking or bending the catheter body.
Another improvement may include increasing the imaging region in the distal tip without increasing the length of the distal tip. The drive cable with the imaging device is moved forward into a space in the distal portion created by removing some internal portion or portions of the distal portion of the primary lumen. Thus, the imaging plane can penetrate deeper into the vasculature, effectively moving the imaging plane distally.
In one aspect of the present invention, an improved catheter system of the type including (a) a tubular catheter body having a proximal portion, a distal portion, and a lumen therethrough; and (b) a drive cable rotatably received in the lumen, is provided. The improved catheter system includes a hub assembly secured to a proximal end of the drive cable. The hub assembly includes a rotary transformer, which has a first ferrite core and a second ferrite core. The second ferrite core contacts the first ferrite core with substantially zero clearance therebetween, as defined above, to promote electrical induction between each core.
In another aspect, an improved catheter system of the type including (a) a tubular catheter body having a proximal portion, a distal portion, and a primary lumen therethrough; and (b) a drive cable having a cable body and a cable lumen rotatably received in the lumen, where the drive cable has at least one lead wire disposed in the cable lumen. The improvement includes a support member disposed proximate to the lead wire to provide strain relief to the lead wire when the lead wire is subjected to a tensile force. The support member can withstand larger tensile forces than the lead wires. Usually, the support member can withstand at least about 100% to 200% more tension than the lead wires, preferably at least about 300%. The support member extends substantially the entire length of the lead wire, usually about 75% to 85% of the length, preferably about 95% to 100%.
In yet another aspect, an improved catheter system of the type including (a) a tubular catheter body having a proximal portion, a distal portion, and a primary lumen therethrough; and (b) a drive cable having a cable body and a cable lumen rotatably received in the primary lumen, where the drive cable has at least one lead wire disposed in the cable lumen, is provided. The improvement includes a strain relief device coupled to a portion of the drive cable. The strain relief device causes the lead wires to be biased, typically with a spring or similar device, such that the lead wires can extend or retract from within the drive cable. The movement of the lead wires keeps the lead wire from being directly subjected to tensile forces which may cause the lead wires to break.
In yet another aspect, an improved catheter system of the type including (a) a tubular catheter body having a proximal tubular portion, a distal tubular portion, and a lumen therethrough, and (b) a drive cable rotatably received in the lumen, is provided. The improvement includes an intermediate tubular portion formed on the tubular catheter body from a transitional material. The intermediate portion can be placed between two portions on the tubular catheter body having similar or dissimilar flexural stiffnesses and/or strengths. Preferably, the transitional material has a greater flexural stiffness than the distal tubular portion and a lower flexural stiffness than the proximal tubular portion. Generally, the intermediate portion can have a flexural stiffness of between 50 kpsi and 200 kpsi, preferably between about 150 kpsi and 190 kpsi.
In yet another aspect, an improved catheter system is provided of the type including (a) a tubular catheter body having a proximal portion, a distal portion, and a primary lumen therethrough, (b) a guidewire lumen coupled coaxially with the primary lumen on the distal portion of the catheter with a wedge in between each lumen; and (c) a drive cable rotatably received in the primary lumen. The improvement includes a wedge lumen formed in the wedge to allow communication between the primary lumen and the guidewire lumen. The wedge lumen is preferably smaller in diameter than the primary lumen. The wedge lumen is preferably between about 0.01 in. and 0.3 in. in diameter, preferably between about 0.012 in. and 0.1 in.
In yet another aspect, an improved catheter system is provided of the type including a tubular catheter body having a proximal portion, a distal portion, and a lumen therebetween, where the lumen is capable of rotatably receiving a drive cable therethrough. The improvement includes a drive cable which has an inner coil and an outer coil. The coils being wound in opposing directions so that the inner coil expands when the drive cable is rotated and where the outer coil contracts when the drive cable is rotated.
In yet another embodiment, an improved catheter system is provided of the type including a tubular catheter body having a proximal portion, a distal portion, and a lumen therethrough. The improvement comprises a first tubular member and a second tubular member arranged in a telescoping engagement, where the first tubular member is formed at least in part from a material, comprising a plastic or a polymer material, such as polyetheretherketone (PEEK).